1. Field of the Invention
The present invention relates to a microcomputer runaway monitoring device.
2. Description of the Conventional Art
There has been conventionally known a microcomputer runaway monitoring device which makes microcomputers including a main microcomputer and a sub microcomputer execute processes in parallel, and detects and resets an abnormality in each of the corresponding microcomputers between both the microcomputers. The microcomputer runaway monitoring device is proposed, for example, in Japanese Unexamined Patent Publication No. 63-313247 and Japanese Unexamined Patent Publication No. 2005-49312.
The conventional microcomputer runaway monitoring device as proposed in the documents is structured, for example, as shown in FIG. 4, such that in a clocking device which actuates a main microcomputer 1a operating in a first operation cycle on the basis of a clock signal output from a first oscillation element 4a, and a sub microcomputer 2a operating in a second operation cycle on the basis of a clock signal output from a second oscillation element 5a in parallel, and carries out a predetermined clocking processing by the main microcomputer 1a and the sub microcomputer 2a, the main microcomputer 1a has a unit configured to output a first pulse signal having a predetermined frequency according to the clocking processing on the basis of the first operation cycle, the sub microcomputer 2a inputs the first pulse signal and has a frequency calculating unit configured to calculate a frequency of the first pulse signal according to the clocking processing on the basis of the second operation cycle, and the sub microcomputer 2a outputs a first pulse signal (Pu1_sig) to the main microcomputer 1a. The main microcomputer 1 is structured such as to calculate a frequency of the first pulse signal (Pu1_sig), stop an output of a second pulse signal (Pu2_sig) in relation to a watch dog timer (WDT) 3 so as to output a reset signal (RS_sig) to a reset terminal (RSTm) of the main microcomputer 1a and a reset terminal (RSTs) of the sub microcomputer 2a from the watch dog timer (WDT) 3 in the case that the calculated frequency (Pu1_fc) deviates from a normal frequency range.
However, according to the microcomputer runaway monitoring device as proposed in the documents mentioned above, in the case that the abnormality is detected in any of the main microcomputer or the sub microcomputer, both of the main microcomputer and the sub microcomputer are simultaneously reset, so that there is a problem that the normal microcomputer is also reset. Further, in the case that the abnormality is generated in the main microcomputer, it is impossible to discriminate whether the sub microcomputer is normal or abnormal.
Further, in the microcomputer runaway monitoring device as proposed in the documents mentioned above, it is necessary to synchronize the frequencies of the main microcomputer and the sub microcomputer in relation to the oscillation elements used in an oscillating circuit, and it is necessary to use the oscillation elements having the same material and the same frequency capacity as the oscillation elements used in the main microcomputer and the sub microcomputer. Accordingly, a total cost increase is caused in the case that an expensive oscillation element is used in one as well as a limitation of parts selectivity is caused.